Elective 1.1: Regulation of Water Content - Problems

Question 1

The graph below shows the rates of filtration and reabsorption of glucose in a healthy kidney at different blood glucose concentrations.
Describe and explain the change in the rate of reabsorption of glucose at different blood glucose concentrations. (3)

Answer 1

When the blood glucose concentration is below 400 units, the rate of reabsorption increases with the blood glucose concentration.
When the blood glucose concentration is higher than 400 units, the rate of reabsorption levels off.
Glucose is reabsorbed through carrier proteins. The rate of reabsorption increases with the blood glucose concentration until all the carrier proteins are occupied by glucose.

Question 2

The graph below shows the rates of filtration and reabsorption of glucose in a healthy kidney at different blood glucose concentrations.
State and explain the blood glucose concentration above which glucose starts to appear in the urine. (3)

Answer 2

180 units
When the blood glucose concentration is above this point, the rate of filtration is higher than the rate of reabsorption.
This suggests that some glucose remains in the glomerular filtrate and thus glucose appears in the urine.

Question 3

The graph below shows the changes in the concentrations of glucose, protein and substance P along the nephron.
Identify region X and explain. (3)

Answer 3

Glomerulus
The protein concentration drops to zero in region Y.
This suggests that proteins cannot pass from region X to region Y.

Question 4

The graph below shows the changes in the concentrations of glucose, protein and substance P along the nephron.
The cells in region Y contain numerous mitochondria. Explain how this feature is related to the change in glucose concentration in region Y. (3)

Answer 4

Mitochondria are the site of aerobic respiration.
The presence of numerous mitochondria in the cells in region Y ensures that enough energy is provided,
for the active transport of glucose.

Question 5

The graph below shows the changes in the concentrations of glucose, protein and substance P along the nephron.
Suggest and explain what substance P may be. (2)

Answer 5

Urea,
as the concentration of substance P increases along the kidney tubule.

Question 6

The graph below shows the changes in the concentrations of glucose, protein and substance P along the nephron.
Explain the difference in composition of a urine of an untreated diabetic patient and a healthy person. (2)

Answer 6

The urine of the diabetic patient would contain glucose, while the urine of the healthy person would not.
The high blood glucose concentration in the patient will result in high concentration of glucose in the glomerular filtrate after ultrafiltration, which exceeds the maximum glucose reabsorption capacity in the kidneys. Some glucose that cannot be transported along the first coiled tubule of the nephron will be removed with the urine formed.

Question 7

CE 2006 I Q9a

The table below shows some information about the composition of the plasma, glomerular filtrate and urine of a healthy person.
Find and account for the percentage change in urea content of urine when compared with that of glomerular filtrate. (2)

Answer 7

Percentage change: 6566.7%
The urea content in urine is much higher because a larger proportion of water is reabsorbed compared to that of urea.

Question 8

CE 2006 I Q9a

The table below shows some information about the composition of the plasma, glomerular filtrate and urine of a healthy person.
Account for the difference in water content between the plasma and the glomerular filtrate. (3)

Answer 8

The water content of glomerular filtrate is greater than that of the plasma,
because plasma proteins and blood cells are too large in size to pass the wall of the glomerulus and that of the Bowman’s capsule.
Therefore, there is a larger proportion of water in the glomerular filtrate compared to that of the plasma.

Question 9

CE 2006 I Q9a

The table below shows some information about the composition of the plasma, glomerular filtrate and urine of a healthy person.
With reference to the cause of diabetes, explain why the urine of a diabetic patient contains glucose. (4)

Answer 9

The person cannot produce sufficient insulin,
to stimulate liver cells to convert glucose into glycogen.
The level of glucose in the blood may exceed the maximum reabsorption capacity in the kidneys,
that glucose cannot be completely reabsorbed in the kidney.
Thus some glucose appears in the urine.

Question 10

The concentrations of glucose and sodium ions in the filtrates in the Bowman’s capsule and first coiled tubule of a healthy kidney were compared with the plasma and expressed as filtrate:plasma ratios. The kidney was then treated with chemical X and the ratio of glucose was measured again. The graph below shows the results.
Explain why the filtrate:plasma ratios of glucose and sodium ions in the Bowman’s capsule are 1.0. (2)

Answer 10

Due to the small molecular size of glucose and sodium ions, they are forced out from the glomerulus into the Bowman’s capsule.
Therefore, the filtrate has the same concentrations of glucose and sodium ions as the plasma, making the filtrate:plasma ratio equal to 1.0.

Question 11

The concentrations of glucose and sodium ions in the filtrates in the Bowman’s capsule and first coiled tubule of a healthy kidney were compared with the plasma and expressed as filtrate:plasma ratios. The kidney was then treated with chemical X and the ratio of glucose was measured again. The graph below shows the results.
Explain the difference between the filtrate:plasma ratio of glucose and that of sodium ions in the first coiled tubule. (2)

Answer 11

The filtrate:plasma ratio of glucose decreases to zero along the first coiled tubule because all glucose in the glomerular filtrate is reabsorbed along the tubule.
The filtrate:plasma ratio of sodium ions remains unchanged because the same proportion of sodium ions and water is reabsorbed along the tubule.

Question 12

The concentrations of glucose and sodium ions in the filtrates in the Bowman’s capsule and first coiled tubule of a healthy kidney were compared with the plasma and expressed as filtrate:plasma ratios. The kidney was then treated with chemical X and the ratio of glucose was measured again. The graph below shows the results.
Suggest and explain the effect of chemical X on the kidney. (3)

Answer 12

The filtrate:plasma ratio of glucose in the kidney treated with chemical X increases along the first coiled tubule.
That means the concentration of glucose in the filtrate increases along the first coiled tubule, as a smaller proportion of glucose is reabsorbed compared to water in the first coiled tubule.
This suggests that chemical X can slow down / prevent the reabsorption of glucose in the first coiled tubule.

Question 13

DSE 2016 II Q1b

The graph below shows the renal glucose handling capability (reabsorption and excretion) in a healthy person and in a patient suffering from type II diabetes.
Describe the change in the renal handling of glucose in the healthy person if the plasma glucose concentration increases from 0 to 280 mg dL^-1.

Answer 13

The glucose reabsorption increases with the plasma glucose concentration,
as it increases between 0 - 200 mg dL^-1,
while no glucose is excreted.
Beyond 200 mg dL^-1, the reabsorption of glucose **levels off*
and excretion of glucose in urine begins and increases with the rise in plasma glucose concentration.

Question 14

DSE 2016 II Q1b

The graph below shows the renal glucose handling capability (reabsorption and excretion) in a healthy person and in a patient suffering from type II diabetes.
It is noted that there is an increased expression of a gene coding for membrane glucose carriers in the kidney tubules of type II diabetic patients.
State the region of the kidney tubules in which the membrane glucose carriers are located.

Answer 14

First coiled tubule

Question 15

DSE 2016 II Q1b

The graph below shows the renal glucose handling capability (reabsorption and excretion) in a healthy person and in a patient suffering from type II diabetes.
It is noted that there is an increased expression of a gene coding for membrane glucose carriers in the kidney tubules of type II diabetic patients.
Suggest why the type II diabetic patient has a higher glucose reabsorption capability.

Answer 15

The expression of the gene resulted in a greater number of glucose transporters at the first coiled tubule.
Hence, the rate of glucose reabsorption from the glomerular filtrate to the blood at the first coiled tubule is higher.

Question 16

DSE 2016 II Q1b

The graph below shows the renal glucose handling capability (reabsorption and excretion) in a healthy person and in a patient suffering from type II diabetes.
If the diabetic condition of the patient is not properly managed, the plasma glucose concentration can rise to a level beyond 300 mg dL^-1. Explain why diabetic patients urinate more frequently than healthy persons. (4)

Answer 16

In diabetic patients, some glucose remains in the glomerular filtrate.
Hence the glomerular filtrate of diabetic patients has a lower water potential than that of healthy people.
As a result, a smaller proportion of water can be reabsorbed back at the collecting duct into the blood.
A larger volume of urine will be produced, and they need to urinate more frequently.

Question 17

The bar chart below shows the amount of water lost by a person on two days. The person was completely at rest on the first day and performed exercise on the second day.
Explain why there was more water lost in sweat and exhaled air on the second day. (2)

Answer 17

The person performed exercise on the second day. During exercise, more sweat was produced to help remove heat generated by muscle cells.
The rate and depth of breathing also increased during exercise. Hence, more water was lost as water vapour in the exhaled air.

Question 18

The bar chart below shows the amount of water lost by a person on two days. The person was completely at rest on the first day and performed exercise on the second day.
Explain why there was less water lost in urine on the second day. (5)

Answer 18

The water potential of the blood decreased due to the water loss in sweat and exhaled air.
The decrease in water potential is detected by osmoreceptors in hypothalamus.
The hypothalamus then stimulates the pituitary gland to release more ADH into the blood.
More ADH will cause the wall of the second coiled tubule and collecting duct to become more permeable to water.
A larger proportion of water in the glomerular filtrate is reabsorbed into the blood. As a result, a smaller volume of more concentrated urine is produced.

Question 19

The bar chart below shows the amount of water lost by a person on two days. The person was completely at rest on the first day and performed exercise on the second day.
Explain why the amount of water lost in faeces remained unchanged during the two days. (1)

Answer 19

Water absorption in the intestine was not affected by exercise.

Question 20

In our body, the water potential of the blood is kept stable so that cells can function properly to sustain life. When the water potential of the blood falls and becomes lower than normal, more ADH will be released from endocrine gland X into the blood.
Explain the meaning of the term “water potential” and describe how the water potential of a solution is affected by is more solvents are added. (2)

Answer 20

The term ‘water potential’ describes the tendency of water molecules to move from one place to another.
Adding more solutes into a solution will decrease the water potential of the solution.

Question 21

In our body, the water potential of the blood is kept stable so that cells can function properly to sustain life. When the water potential of the blood falls and becomes lower than normal, more ADH will be released from endocrine gland X into the blood.
Name endocrine gland X. (1)

Answer 21

Pituitary gland

Question 22

In our body, the water potential of the blood is kept stable so that cells can function properly to sustain life. When the water potential of the blood falls and becomes lower than normal, more ADH will be released from endocrine gland X into the blood.
Explain how releasing more ADH from endocrine gland X restores the water potential when the water potential of the blood becomes lower than normal. (3)

Answer 22

The increased level of ADH in the blood causes the walls of the second coiled tubule and collecting duct of the nephron to become more permeable to water.
Thus, a larger proportion of water is reabsorbed from the glomerular filtrate.
As a result, a smaller volume of concentrated urine is produced. As less water is lost as urine, the water potential of the blood rises and returns to normal.

Question 23

In our body, the water potential of the blood is kept stable so that cells can function properly to sustain life. When the water potential of the blood falls and becomes lower than normal, more ADH will be released from endocrine gland X into the blood.
Diabetes insipidus is a disorder that affects a person’s ability to control the water balance in the body. It may be caused by the failure of endocrine gland X to release sufficient ADH or the kidney tubules do not respond to ADH. List 2 possible symptoms of diabetes insipidus patients. (2)

Answer 23

The patients produce large amounts of dilute urine each day and suffer from dehydration.

Question 24

CCEA GCE(A) 2012

The graph below shows the level of ADH in a student’s blood over a three hour period after drinking 0.5 litres of water.
With reference to the process of osmoregulation, explain fully the changes in ADH concentration. (4)

Answer 24

The concentration of ADH decreases during the first hour. This is because after drinking 0.5 litres of water, the water potential of the blood increases.
The increased water potential of the blood is detected by osmoreceptors in the hypothalamus. The hypothalamus inhibits the pituitary gland and the pituitary gland releases less ADH into the blood.
The concentration of ADH starts to increase after one hour and returns to normal level after 2.5 hours. This is because as more water is lost as urine, the water potential of the blood falls.
The decreased water potential of the blood is detected by osmoreceptors in the hypothalamus. The hypothalamus stimulates the pituitary gland to release more ADH into the blood.

Question 25

#CCEA GCE(A) 2012 The graph below shows the level of ADH in a student's blood over a three hour period after drinking 0.5 litres of water. One symptom of diabetes is the higher than normal glucose in the blood which results in the appearance of glucose in the urine. Suggest an explanation for the presence of glucose in the urine of people with diabetes. (2)

Answer 25

The amount of carrier proteins for the active transport of glucose is **limited** in the first coiled tubule. The high blood glucose concentration in the patient will result in **high concentration of glucose in the glomerular filtrate** after ultrafiltration, which **exceeds the maximum glucose reabsorption capacity** in the kidneys. Some glucose that cannot be transported along the first coiled tubule of the nephron will be removed with the urine formed.

Question 26

#DSE 2014 II Q1a The table below shows the amounts of difference substances handled by the kidneys. With reference to the mechanisms involved in reabsorption, account for the difference in the amount of glucose and urea handled by the kidneys. (4)

Answer 26

**All** glucose filtered in the kidney tubules is reabsorbed into the blood, because it is reabsorbed by means of **active transport**. However, only **half** of the urea is reabsorbed back into the blood, as urea is reabsorbed by means of **diffusion** only.

Question 27

#DSE 2014 II Q1a The table below shows the amounts of difference substances handled by the kidneys. Of the total amount of water reabsorbed by the kidneys, only a small amount if regulated by a hormone. Using the information provided in the table, explain how most of the water is reabsorbed regardless of hormonal control. (3)

Answer 27

As most of the substances in the glomerular filtrate are reabsorbed into the blood, the **water potential of the remaining fluid in the kidney tubules increases** to a value such that the water potential of blood is much lower than that of the remaining fluid. Hence, there is a **net flow of water** from the glomerular filtrate in the kidney tubules to the blood in the blood capillaries by **osmosis**.

Question 28

#DSE 2014 II Q1a The table below shows the amounts of difference substances handled by the kidneys. Of the total amount of water reabsorbed by the kidneys, only a small amount if regulated by a hormone. Name the hormone which is responsible for regulating the reabsorption of water and state how it works. (2)

Answer 28

ADH, it increases the permeability of the collecting duct to water so more water will be reabsorbed.

Question 29

#DSE 2017 II Q1b The diagram below shows a nephron and its associated structures. The solute concentration of the fluid at different positions in the tubules are indicated. With reference to the physiological processes involved, explain why there is no change in the solute concentration of the fluid inside the tubule as the fluid flows from point A to point B. (4)

Answer 29

Useful solutes, e.g. glucose, sodium ion, amino acids, are **reabsorbed** back into the capillary by **active transport** along the first coiled tubule. Hence, the **water potential of the glomerular filtrate increases** to a value which is higher than the blood in the capillaries surrounding the first coiled tubule. As a result, water moves out of the first coiled tubule to the blood **down the water potential gradient by osmosis**. The amount of water reabsorbed is **proportional** to the amount of solutes reabsorbed. Hence, solute concentration remains the same as the fluid flow from point A to point B.

Question 30

#DSE 2017 II Q1b The diagram below shows a nephron and its associated structures. The solute concentration of the fluid at different positions in the tubules are indicated. Account for the difference in the solute concentration of fluid in point D with or without ADH. (3)

Answer 30

Fluid at point D without ADH has a **lower solute concentration** than that with ADH. ADH increases the permeability of the second coiled tubule and the collection duct (D) to water. With ADH, as a result, **a larger proportion of water is reabsorbed** into the blood, and a **smaller amount of more concentrated urine** is produced. Hence there is a higher solute concentration at D with ADH.

Question 31

#DSE 2017 II Q1b The diagram below shows a nephron and its associated structures. The solute concentration of the fluid at different positions in the tubules are indicated. Explain which part of the nephron is most likely damaged if protein is present in the fluid at point D. (2)

Answer 31

The wall of the glomerulus that is associated with the nephron. Protein molecules are **too large in size*** to pass through the wall of glomerulus. If protein is present in the kidney tubule, it is most likely that the wall of glomerulus is damaged and **becomes permeable** to proteins in blood. Then, some plasma proteins will be **forced out from blood** under high blood pressure in the glomerulus into the Bowman’s capsule in the kidney by **ultrafiltration**, resulting in protein found in the glomerular filtrate.

Question 32

The graph below shows the changes in the relative amounts of glucose, water, and substance X along the kidney tubule of a healthy person. Substance X is a drug injected into the person to measure the filtration rate of the glomerulus. With reference to the graph, explain why substance X can be used to measure the filtration rate of the glomerulus. (2)

Answer 32

Substance X is **not reabsorbed** by the kidney. Thus, the **rate of excretion of substance X** in the urine will be proportional to the **filtration rate** of the glomerulus.

Question 33

The graph below shows the changes in the relative amounts of glucose, water, and substance X along the kidney tubule of a healthy person. Substance X is a drug injected into the person to measure the filtration rate of the glomerulus. Explain how the curve of water will change along the kidney tubule if ADH is injected into the person. (3)

Answer 33

The curve in the portions of the second coiled tubule and collecting duct would be lower. This is because ADH increases the permeability of the walls of the second coiled tubule and collecting duct to water. A **larger proportion of water** is reabsorbed and the relative amount of water in the fluid in the kidney tubule decreases.

Question 34

The graph below shows the changes in the relative amounts of glucose, water, and substance X along the kidney tubule of a healthy person. Substance X is a drug injected into the person to measure the filtration rate of the glomerulus. Suggest why the second coiled tubules often become damaged in diabetics. (3)

Answer 34

In diabetics, the blood glucose level and the glucose content in the glomerular filtrate **exceeds the maximum reabsorption capacity** in the kidneys, thus glucose **cannot be reabsorbed completely** in the first coiled tubule. The water potential of the filtrate in the second coiled tubule becomes **lower than that of the cytoplasm of the cells of the second coiled tubule** due to the presence of glucose. There is a **net movement of water down the water potential gradient**, and water leaves the cytoplasm of the cells of the second coiled tubule by **osmosis**, causing dehydration and damage to the cells in the second coiled tubule.

Question 35

#DSE 2012 II Q1a In a study about the replenishment of water after exercise, participants performed exercise until they lost 1500mL of water. They were then divided into 3 groups and asked to consume a 2000mL sports drink containing 0, 50, and 100 mmol/L sodium respectively. Urine samples were collected at 1-hour intervals for 6 hors and the net body fluid balance throughout the course of the experiment was determined. The results are respectively shown in the figures. Describe the general patterns of the urine output after consuming drinks with different sodium concentrations. (4)

Answer 35

Regardless of the sodium concentration of the drinks, the greatest urine output occurred over the 1st hour. The urine output then dropped continuously, until the 5th hour, the urine output became more or less the same. The urine output of the participants who consumed drinks with higher sodium content were usually smaller than those participants who consumed drinks with lower sodium content.

Question 36

#DSE 2012 II Q1a In a study about the replenishment of water after exercise, participants performed exercise until they lost 1500mL of water. They were then divided into 3 groups and asked to consume a 2000mL sports drink containing 0, 50, and 100 mmol/L sodium respectively. Urine samples were collected at 1-hour intervals for 6 hors and the net body fluid balance throughout the course of the experiment was determined. The results are respectively shown in the figures. Account for the high urine output of the participants who consumed sports drink with 0 mmol/L sodium. (4)

Answer 36

After drinking the sports drink with 0 mmol / L sodium, the water potential of the blood **increases** and the increase is detected by the osmoreceptors in the hypothalamus. The hypothalamus then **stimulates the pituitary gland** to release **less ADH** into the blood circulation. As a result, the wall of the collecting ducts of the kidney tubule became less permeable to water. Thus, a **smaller proportion of water was reabsorbed** and hence, the volume of urine output increased.

Question 37

#DSE 2012 II Q1a In a study about the replenishment of water after exercise, participants performed exercise until they lost 1500mL of water. They were then divided into 3 groups and asked to consume a 2000mL sports drink containing 0, 50, and 100 mmol/L sodium respectively. Urine samples were collected at 1-hour intervals for 6 hors and the net body fluid balance throughout the course of the experiment was determined. The results are respectively shown in the figures. Explain which sports drink is recommended to athletes after exercise in terms of replenishment of water. (3)

Answer 37

The sports drink with 100 mmol / L sodium. It leads to a relatively smaller urine output among the 3 drinks, indicating that the body retains more water after drinking. Also, the **net fluid balance** remains high than 0 throughout the course of the experiment.

Question 38

#DSE 2018 II Q1a In a study of the effect of consuming different liquids on urine production, three groups of healthy persons were asked to follow the same pattern of physical activity and dietary intake. After that, Group A consumed a 1500 mL alcoholic beverage, Group B consumed 1500 mL water and Group C did not consume any liquid. Their urine was collected and its volume measured at 60-minute intervals over a period of 240 minutes. The results are shown in the graph below. With reference to the hormonal control of osmoregulation, explain why Group C had a much lower average volume of urine produced than Group A and Group B. (5)

Answer 38

Group C did not drink any liquid in the experiment, therefore the **water potential of the blood** in persons in group C was **lower** than that of the groups A and B. This was detected by the osmoreceptors in the hypothalamus. The hypothalamus then stimulated the pituitary gland to **release more ADH** into the blood. More ADH resulted in **higher permeability** of collecting duct of the nephron to water. As a result, a **larger proportion of water** was reabsorbed at the collecting duct, and less urine was produced.

Question 39

#DSE 2018 II Q1a In a study of the effect of consuming different liquids on urine production, three groups of healthy persons were asked to follow the same pattern of physical activity and dietary intake. After that, Group A consumed a 1500 mL alcoholic beverage, Group B consumed 1500 mL water and Group C did not consume any liquid. Their urine was collected and its volume measured at 60-minute intervals over a period of 240 minutes. The results are shown in the graph below. State the effect of consuming alcoholic beverages on urine production with reference to the results of Group A and Group B, and deduce one possible effect of alcohol on the hormonal control of osmoregulation. (1+1)

Answer 39

Alcohol consumption resulted in the production of more urine. More urine production suggested that the release / production of ADH might have been inhibited by alcohol.

Question 40

#DSE 2018 II Q1a In a study of the effect of consuming different liquids on urine production, three groups of healthy persons were asked to follow the same pattern of physical activity and dietary intake. After that, Group A consumed a 1500 mL alcoholic beverage, Group B consumed 1500 mL water and Group C did not consume any liquid. Their urine was collected and its volume measured at 60-minute intervals over a period of 240 minutes. The results are shown in the graph below. Explain why the participants should avoid doing vigorous physical activity during the study. (2)

Answer 40

This prevents the participants from losing water through **sweating**, or as **water vapour** during rapid breathing when performing high physical activity, as this may **reduce the urine production of each individual to different extents**, resulting in **no valid comparison** of results.

Question 41

Peritoneal dialysis is a method to treat kidney failure. Its working principle is similar to that of haemodialysis. In peritoneal dialysis, the peritoneum (lining of the abdominal cavity) is used as the dialysis membrane. The diagram below shows the process of peritoneal dialysis. The table below shows the concentrations of different solutes in the dialysing fluid and in the blood of a patient with kidney failure. With reference to the table, suggest which substance(s) in the table can be removed from the blood of the patient during dialysis, and explain how it can be done. (1+3)

Answer 41

Sodium ions and urea. The peritoneum has many **small pores** that allow sodium ions and urea to pass through freely. As the concentrations of sodium ions and urea in the blood are **higher** than those in the dialysing fluid, sodium ions and urea **travel down the concentration gradient and diffuse** from the blood into the dialysing fluid.

Question 42

Peritoneal dialysis is a method to treat kidney failure. Its working principle is similar to that of haemodialysis. In peritoneal dialysis, the peritoneum (lining of the abdominal cavity) is used as the dialysis membrane. The diagram below shows the process of peritoneal dialysis. The table below shows the concentrations of different solutes in the dialysing fluid and in the blood of a patient with kidney failure. Explain why the dialysing fluid needs to stay in the abdominal cavity for about 4 hours during the treatment. (1)

Answer 42

This provides enough time to remove wastes from the blood.

Question 43

Peritoneal dialysis is a method to treat kidney failure. Its working principle is similar to that of haemodialysis. In peritoneal dialysis, the peritoneum (lining of the abdominal cavity) is used as the dialysis membrane. The diagram below shows the process of peritoneal dialysis. The table below shows the concentrations of different solutes in the dialysing fluid and in the blood of a patient with kidney failure. Explain why patients receiving peritoneal dialysis require more frequent dialysis compared with patients receiving haemodialysis. (3)

Answer 43

The dialysing fluid is **constantly refreshed in haemodialysis**, but not in peritoneal dialysis. The **steep concentration gradient** of metabolic wastes like urea between the blood and the dialysing fluid in peritoneal dialysis **cannot be maintained** over the course of treatment. Therefore, the **rate of diffusion** of waste from the blood to the dialysing fluid decreases; **fewer wastes can be removed** per treatment and more frequent dialysis is needed.

Question 44

Peritoneal dialysis is a method to treat kidney failure. Its working principle is similar to that of haemodialysis. In peritoneal dialysis, the peritoneum (lining of the abdominal cavity) is used as the dialysis membrane. The diagram below shows the process of peritoneal dialysis. The table below shows the concentrations of different solutes in the dialysing fluid and in the blood of a patient with kidney failure. Dialysing fluid with different concentrations of glucose (1.5%, 2.5%, or 4.25%) are available. Suggest and explain which dialysing fluid is more suitable for a patient is they have a walk on a hot day. (4)

Answer 44

Dialysing fluid with 1.5% glucose. The patient may have **lost a lot of water due to sweating** during the walk, which **decreases the water potential** of their blood. Dialysing fluid with 1.5% glucose has the **highest water potential**. Therefore, it will remove the least water from the blood by osmosis and **keep the most water** in the patient’s body.

Question 45

Patients with kidney failure can use a kidney machine to help remove metabolic wastes from the blood. The diagram below shows the working principle of a kidney machine. With reference to the diagram, describe and explain two features that allow the machine to remove metabolic wastes from the blood effectively. (4)

Answer 45

The kidney machine contains **many pieces** of dialysis tubing. This increases the **surface area** for the diffusion of metabolic wastes. The blood and the dialysing fluid **flow in opposite directions**. This maintains the **steep concentration gradient** of metabolic wastes between the blood and the dialysing fluid, facilitating diffusion of metabolic wastes from the blood to the dialysing fluid through the dialysis tubing.

Question 46

Patients with kidney failure can use a kidney machine to help remove metabolic wastes from the blood. The diagram below shows the working principle of a kidney machine. Before receiving haemodialysis, the patient may need to undergo a surgery to connect an artery to a vein in the arm as shown in the diagram. The photograph below shows the appearance of the vein after the surgery. Explain why the vein becomes larger after the surgery, and suggest two advantages of having an enlarged vein during dialysis. (2+2)

Answer 46

The blood pressure in the artery is **higher** than that in the vein; after the surgery, blood from the artery with high blood pressure flows to the vein directly through the connection. The vein **does not have a muscular wall as thick as that of the artery** to withstand the high blood pressure. The high blood pressure causes the vein to **distend**. Advantages: 1. This allows the doctor to insert the needles for dialysis more easily. 2. This allows blood to move out and back into the patient’s body more quickly.

Question 47

Patients with kidney failure can use a kidney machine to help remove metabolic wastes from the blood. The diagram below shows the working principle of a kidney machine. Suggest why patients with kidney diseases are advised to avoid excess intake of proteins. (3)

Answer 47

Proteins are broken down into **amino acids** in the body. Excess amino acids will be broken down in the liver and **urea** is formed in this process. Since patients with kidney diseases **cannot remove urea effectively** from their body, urea, which is harmful, accumulates in the body.

Question 48

Patients with kidney failure can use a kidney machine to help remove metabolic wastes from the blood. The diagram below shows the working principle of a kidney machine. Kidney transplantation is another method to treat kidney failure. State one advantage and one disadvantage of kidney transplantation compared with the use of kidney machines. (2)

Answer 48

Advantage: Kidney transplantation needs to be done once only / saves time / saves resources. Disadvantage: The risk of kidney transplantation is higher. / The transplanted organ may be rejected by the patient’s body. / Finding a suitable kidney for transplantation is difficult.

Question 49

#DSE Sample Paper II Q1b The diagram below shows the structure of a nephron. Explain why the fluid in A has a lower percentage of glucose but a higher percentage of urea than that in B. (2)

Answer 49

When the fluid passes from B to A, **all glucose will be reabsorbed** in the first coiled tubule, so no glucose is present in the fluid in A. A **larger proportion of water is reabsorbed** compared to urea, so the percentage of urea in A is higher than that in B.

Question 50

#DSE Sample Paper II Q1b The diagram below shows the structure of a nephron. Explain the change in the concentration of the fluid in A after heavy sweating. (5)

Answer 50

After the loss of much water in heavy sweating, the **water potential of the blood decreases**. This is detected by **osmoreceptors in the hypothalamus**. The hypothalamus then stimulates the pituitary gland to **release more ADH**. **More ADH** increases the permeability of the second coiled tubule and the collecting duct to water. Thus **a greater proportion of water** will be reabsorbed from the fluid in A into the blood by **osmosis**. As a result, the concentration of the fluid in A **increases**.

Question 51

#DSE Sample Paper II Q1b The diagram below shows the structure of a nephron. Patients suffering from kidney failure may need to receive treatments involving a dialysis machine which works on similar biological principles as the kidney. State one similarity and one difference between the functioning of the artificial membrane in the dialysis machine and that of the wall of nephrons. (2)

Answer 51

Similarity: Both the dialysis membrane and the wall of the nephron are **differentially permeable**, allowing small molecules such as urea and other waste materials to pass through. but not plasma proteins and blood cells. Difference: The cells of the wall of the nephron **actively reabsorb useful substances** (e.g. glucose) into the blood by **active transport**, while the dialysis membrane has no such function.

Question 52

The diagram shows a human nephron. The table shows the concentration of some substances in the fluid content in structures P, Q and R in a person. Name structures P, Q and R. Name fluids X, Y and Z. (6)

Answer 52

P: Glomerulus Q: Bowman’s capsule R: Collecting duct X: Blood plasma (not blood) Y: Urine Z: Glomerular filtrate

Question 53

The diagram shows a human nephron. The table shows the concentration of some substances in the fluid content in structures P, Q and R in a person. Explain the deduction on the region from which fluid X was taken. (2)

Answer 53

Protein is present in X but absent in Y and Z. This shows that X (blood plasma) is taken from P (glomerulus) because plasma proteins in P are too large to pass through the **differentially permeable wall** of P to enter Q and R.

Question 54

The diagram shows a human nephron. The table shows the concentration of some substances in the fluid content in structures P, Q and R in a person. Explain two reasons on the deduction on the region from which fluid Y was taken. (4)

Answer 54

Glucose is present in both X and Z but not in Y. This shows that Y (urine) is taken from R (collecting duct) because glucose found in the glomerular filtrate entering the nephron should be **completely reabsorbed into the surrounding blood of the nephron by active transport**. Also, the concentration of urea in Y is higher than that in X and Z. This indicates that Y (urine) is taken from R (collecting duct) because the **proportion of water reabsorbed** along the kidney tubule is **higher than the proportion of urea reabsorbed**, leading to higher urea concentration of Y compared to X and Z.

Question 55

The diagram shows a human nephron. The table shows the concentration of some substances in the fluid content in structures P, Q and R in a person. With reference to letters from the diagram, explain the difference between the water content in X and Z. (4)

Answer 55

The water content in X (blood plasma) is **lower** than that of Z (glomerular filtrate). This is because of there are **plasma proteins** in X, which are **too large in size** to pass through the differentially permeable wall of P (glomerulus), and hence are not found in Z. Thus, there is a **higher proportion of water** in Z formed from ultrafiltration as compared to X.

Question 56

The diagram below shows a human nephron. Predict and explain the change in the concentration of salts in structure R after the person has drunk a large amount of water. (6)

Answer 56

After the person has drunk a large amount of water, the **water absorbed will increase the water potential of their blood**. The increased water potential of the blood is detected by **osmoreceptors in the hypothalamus**. The hypothalamus then stimulates the pituitary gland to **release less ADH**. **Less ADH** causes the walls of the second coiled tubule and structure R in the kidney become **less permeable to water**, so a **smaller proportion of water** will be reabsorbed along these regions of the nephron into the surrounding blood. Thus an **increased volume of water with a decreased salt concentration** will be **retained in R** to be excreted as urine.

Question 57

If a person loses 450 mL of blood and then drank 450 mL of distilled water, explain why their blood volume cannot be restored to 100% even after 2 hours. (6)

Answer 57

Drinking distilled water **increases the water potential of the blood** significantly. The increase in water potential of blood would be detected by **osmoreceptors in the hypothalamus**. The hypothalamus will then stimulate the pituitary gland to **release less ADH** into the blood. **Less ADH** causes the walls of the second coiled tubule and the collecting duct to water to be less permeable to water. A **smaller proportion of water is reabsorbed** from the fluid in the second coiled tubule and the collecting duct into the blood surrounding these tubules. Thus, **a fair proportion of water drunk will be removed in the urine**. Thus, the blood volume will not be restored by 100%.

Question 58

In a study, a diabetic patient drank the same volume and concentration of a glucose solution as a healthy person. Their urine output and content was then measured. Explain why a diabetic patient would have glucose in his urine. (3)

Answer 58

The high blood glucose concentration in the patient will result in **high concentration of glucose in the glomerular filtrate after ultrafiltration**, which exceeds the **maximum glucose reabsorption capacity** in the kidneys. Some glucose that cannot be transported along the first coiled tubule of the nephron will be removed with the urine formed.

Question 59

In a study, a diabetic patient drank the same volume and concentration of a glucose solution as a healthy person. Their urine output and content was then measured. Explain why it is important that both individuals remain at rest throughout the investigation. (3)

Answer 59

This prevents the loss of water through **sweating**, or as **water vapour** during rapid breathing when performing high physical activity. This is because these sources of water loss may **reduce the volume of urine produced to different extents** in terms of healthy person and the diabetic, and therefore **no valid comparison of results** can be made.

Question 60

In a study, a diabetic patient drank the same volume and concentration of a glucose solution as a healthy person. Their urine output and content was then measured. Explain why the diabetic patient has a larger volume of urine produced than a healthy person. (6)

Answer 60

Diabetic patients have a **prolonged high blood glucose level** which **exceeds the maximum glucose reabsorption capacity** in the kidneys. Thus the patient fails to reabsorb all glucose from the glomerular filtrate in the kidney tubule, resulting in some **glucose remaining in the glomerular filtrate**. This causes their glomerular filtrate to **have a lower water potential** than that of healthy people after drinking the same volume and concentration of a glucose solution. A **smaller proportion of water** in the filtrate can be reabsorbed back into the blood along the kidney tubule by **osmosis** by the diabetic patient compared to the healthy person. Therefore, the volume of urine produced (at any particular time interval) by the diabetic patient will be larger than the healthy person.

Question 61

The graph shows the concentrations of protein in the blood plasma in the renal arteries ad in the glomerular filtrate in different parts of the kidney tubule. Describe and explain the changes in the concentrations of protein shown in the graph. (2)

Answer 61

Protein is present in blood plasma in renal artery but absent in the nephron. This is because they are **too large in size** to pass through the differentially permeable membrane of the glomerulus and Bowman's capsule.

Question 62

The graph shows the concentrations of glucose in the blood plasma in the renal arteries ad in the glomerular filtrate in different parts of the kidney tubule. Describe and explain the changes in the concentrations of glucose shown in the graph. (2)

Answer 62

The concentration of glucose in the glomerular filtrate **decreases to zero** as it flows along the first coiled tubule. This is because **all glucose in the glomerular filtrate is reabsorbed** into the blood surrounding the first coiled tubule by **active transport**.

Question 63

The graph shows the concentrations of urea in the blood plasma in the renal arteries ad in the glomerular filtrate in different parts of the kidney tubule. Describe and explain the changes in the concentrations of urea shown in the graph. (3)

Answer 63

The concentration of urea **increases** as the glomerular filtrate flows along the kidney tubule. Although some urea in the filtrate is reabsorbed into the blood surrounding the tubule by **diffusion only**, there is a **larger proportion of water** which is reabsorbed compared to that of urea, which causes the concentration of urea in the glomerular filtrate to increase.

Question 64

The graph shows the concentrations of salt in the blood plasma in the renal arteries ad in the glomerular filtrate in different parts of the kidney tubule. Describe and explain the changes in the concentrations of salt in the first coiled tubule shown in the graph. (5)

Answer 64

In the first coiled tubule, the concentration of salt **remains constant**. This is because salt in the glomerular filtrate is **reabsorbed** into the surrounding blood by diffusion and active transport in the first coiled tubule. This **decreases the water potential of blood** surrounding the tubule and the water potential becomes lower than that of the glomerular filtrate. Thus there is a net movement of water **down the water potential gradient** from the glomerular filtrate into the blood surrounding the tubule by **osmosis**. The **proportion of water reabsorbed** is **the same** as the proportion of salt reabsorbed, so the salt concentration remains constant.

Question 65

The graph shows the concentrations of salt in the blood plasma in the renal arteries ad in the glomerular filtrate in different parts of the kidney tubule. Describe and explain the changes in the concentrations of salt in the loop of Henle, second coiled tubule, and the collecting duct shown in the graph. (2)

Answer 65

The concentration of salt **increases** along the loop of Henle, second coiled tubule, and the collecting duct. The **proportion of water reabsorbed** is **higher than** as the proportion of salt reabsorbed, so the salt concentration increases.

Question 66

A class of students was divide into two groups. After having the same physical activity and diet, group I was given 1500 mL of water to drink while group II was given an equal volume of isotonic salt solution. The urine production of both groups was measured over the next 3 hours. The average cumulative urine production of each student was calculated and the results are shown in the graph below. Explain which fluid is suggested for an athlete after vigorous exercise. (4)

Answer 66

Isotonic salt solution. This is because there is a **lower cumulative urine production** in group II that drank isotonic salt solution **compared to group I** that drank water over 3 hours after drinking. This suggests that **more water can be retained** in the body after drinking the isotonic salt solution, therefore the water lost from the body can be **restored more quickly** after drinking teh isotonic salt solution.

Question 67

Explain which part of the nephron and its associated structures could be damaged if protein is found in the urine. (4)

Answer 67

The wall of the glomerulus that is associated with the nephron. The damaged wall of the glomerulus **becomes permeable to plasma proteins** in the blood. Some plasma proteins are forced out from blood under **high blood pressure** in the glomerulus into the Bowman’s capsule in the kidney by **ultrafiltration**. When proteins in the glomerulus filtrate form due to ultrafiltration **cannot be completely reabsorbed** along the kidney tubules, these proteins will be excreted with urine.

Question 68

Explain why a larger amount of urine is produced after a salty meal. (4)

Answer 68

After consuming a salty meal, more salt is absorbed into the blood plasma **via the small intestine**. The **water potential** of blood and hence the glomerular filtrate decreases / **concentration of salt** in the glomerular filtrate increases. Excess salt is excreted in the urine A **smaller proportion of water is reabsorbed** along the kidney tubules, resulting in a larger volume of urine produced.